[qqrs]

Public key encryption does feel like it could be a useful approach. Rather than putting the burden on camera manufacturers, it could be implemented on a portable hard drive with SD card reader. (Turns out these already exist, just not with encryption: https://www.wdc.com/products/portable-storage/my-passport-wi...)

This would allow the photographer to review photos on the camera until satisfied, then simply plug the SD card into the portable hard drive. All files would be automatically encrypted and saved to the hard drive, and the SD card would be wiped. The files on the hard drive can't be decrypted without the private key, stored at home.